The present invention relates, in general, to apparatus for producing flow modulation epitaxy, and more particularly relates to a high throughput organometallic vapor phase epitaxy (OMVPE) apparatus for deposition of material on substrates. In a preferred embodiment, the invention is directed to a cold wall reactor, which is convertible to a hot wall reactor, for epitaxial deposition of compound semiconductor materials.
Reactors for use in chemical vapor deposition, for example for epitaxial processing of semiconductor materials, or wafers, are generally well known. Two types of reactor are available for epitaxial processing, one being referred to as a cold wall reactor and the other being referred to as a hot wall reactor. Both types are well known, and the particular reactor used depends upon the type of reaction to be performed. For example, silicon processing is normally done in a hot wall reactor device.
In a chemical vapor deposition reactor, the chemicals used in the process have a tendency to decompose on the cell wall as well as on the substrate as they flow through the cell. Layers of decomposed reactants build on the cell wall, and eventually these layers begin to flake off, producing particulate contaminates in the cell which damage the wafer being processed. In addition, certain compounds produce a chemical memory effect; i.e., impurities accumulate on the cell wall, and then are released during a later run, contaminating that later run. To prevent such contamination, the cells must be periodically cleaned. Usually, however, this can only be done by disassembling the device, which not only is time-consuming, but causes the entire cell to become contaminated by the atmosphere. Thus, there is a need for a mechanism for cleaning reactor cells without the need to disassemble them and without risking contamination.
Furthermore, in many chemical vapor deposition reactors a cooling mechanism is provided to reduce the temperature of the hot reactive gases after they have passed over the wafer to be treated and prior to their removal from the reactor by external vacuum equipment. In such devices, however, as the cooled gases flow out of the chamber, the chemicals carried by the gases condense or precipitate onto the vacuum equipment, requiring time consuming and expensive maintenance to avoid serious damage to the equipment. When phosphide compounds are used in reactors of this type, for example in the formation of red lasers, such compounds present an additional problem, for yellow, red or white phosphorous compounds are pyrophoric and spontaneously catch fire if exposed to the atmosphere. If such products precipitate onto the reactor walls or reach the vacuum equipment, opening the reactor to clean it can result in a fire.
Finally, difficulties have been encountered in the gas distribution systems used with various cell geometries, for it is difficult to obtain a proper seal for the reactor chamber, thereby limiting the structural arrangement of the reactor and the consequent flow paths. As a result, many reactor arrangements cause the gases to be directed onto flat surfaces. The gases rebound from such surfaces, resulting in a highly undesirable recirculation of the reactive gases within the chamber. Thus, a simplified reactor geometry having improved fluid dynamics for the gas flowing into the chamber that will avoid recirculation problems is highly desirable.